1. Field of the Invention
This invention relates to a continuous process for the production of a copolymer of an alkali metal vinyl sulfonate, such as sodium vinyl sulfonate, and acrylic acid.
2. Description of the Prior Art
Copolymers of alkali metal vinyl sulfonates, and in particular, sodium vinyl sulfonate, also known as sodium ethylenesulfonate, and acrylic acid are known in the art. Thus, the preparation of a copolymer of sodium vinyl sulfonate and acrylic acid is described by Breslow and Kutner in J. Polymer Science XXVII, 295-312 (1958). The copolymer described therein is obtained in a batch polymerization process in an aqueous medium.
U.S. Pat. No. 3,203,938 to Baechtold discloses a batch polymerization process for the preparation of a copolymer of sodium vinyl sulfonate and acrylic acid or acrylamide in an alcoholic medium in which the copolymer is insoluble. This patent teaches that a high conversion of monomers to polymer is achieved and that the relative mole ratio between the sodium vinyl sulfonate and the acrylamide or acrylic acid in the final composition may be controlled over a wide range.
The use of a batch process for the preparation of a copolymer of sodium vinyl sulfonate and acrylic acid has certain inherent disadvantages. Thus, in such a process, the sodium vinyl sulfonate has an unsatisfactory reactivity ratio with respect to acrylic acid, and the addition of acrylic acid to the sodium vinyl sulfonate must be protracted over an hour in order to attain maximum sodium vinyl sulfonate incorporation. Further, a batch polymerization process requires large and costly equipment which is difficult to move from one place to another.